Conventionally, in the process for manufacturing semiconductor devices, etching that partially cuts a semiconductor wafer or material deposited thereon is frequently used. Plasma patching, sputter etching or reactive ion etching methods are known ways to perform the etchings. In particular, plasma etching uses chemical reaction such that only materials that need to be etched are removed (in other words, selectively etched). For this reason, plasma patching is widely used in the process of manufacturing semiconductor devices.
FIG. 5 shows an illustration to describe a structure of a chamber in which plasma etching is conducted. Electrodes that generate plasma are disposed within the chamber 1, and the electrodes are connected to a high-frequency plasma generation apparatus that is provided outside the chamber. Also, within the same chamber 1, a semiconductor wafer mounting section is provided, such that a semiconductor wafer and material deposited thereon can be etched.
The chamber 1 described above is equipped with a reactive gas supply opening 2 and an exhaust opening 3 as shown in the figure, whereby a reactive gas can be introduced into the chamber 1 under a reduced pressure through a flow quantity control valve 4, and the reactive gas can be exhausted from the chamber 1 by a vacuum pump (not shown) provided in the succeeding stage of the exhaust opening 3. PFC such as CF4, CHF3, C4F8 or the like is used as the reactive gas to conduct an etching of silicon oxide (SiO2) that is used as a dielectric material.
FIG. 6 shows a graph of an operation process of the chamber 1. As shown in the figure, for conducting an etching on a semiconductor wafer within the chamber 1, first, the pressure within the chamber 1 is sufficiently reduced by the vacuum pump (a range {circle around (1)} in the figure), and the flow quantity control valve 4 is opened to introduce a reactive gas into the chamber 1. As the reactive gas is introduced into the chamber 1, the reactive gas is also discharged through the exhaust opening 3. It is noted that, when the reactive gas is introduced, the degree of opening and closing of the flow quantity control valve 4 is adjusted, such that the pressure within the chamber 1 is adjusted to stabilize at a predetermined value (a range {circle around (2)} in the figure).
After the pressure within the chamber 1 is stabilized at the predetermined value, the high frequency plasma generation apparatus is operated to generate plasma of the reactive gas between the electrodes, whereby an etching process for the semiconductor wafer is conducted (a range {circle around (3)} in the figure). When a predetermined time has passed, the flow quantity control valve 4 is closed to stop the supply of the reactive gas, and the high frequency plasma generation apparatus is also stopped to complete the etching process (a range {circle around (4)} in the figure).
However, in the etching process described above, the following problems are encountered. In a preceding stage of the etching (the range {circle around (2)} in the figure), the pressure within the chamber 1 needs to be set at a predetermined value, and a reactive gas that is used for the plasma process is used for setting this value. In other words, during the pressure setting within the chamber, a reactive gas that does not contribute to the plasma etching is exhausted through the exhaust opening 3 into the atmosphere as it is. This results in a higher cost. Further, since the PFC that is used as a reactive gas has a high GWP (global warming potential) that is several thousands—several ten thousands times higher than that of carbon dioxide, it is not preferable for the environment to exhaust the gas into the atmosphere.
The present invention has been made in view of the problems of the conventional art, and it is an object of the present invention to provide a plasma etching method that can suppress discharge of PFC that does not contribute to the plasma etching into the atmosphere.